The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Thursday, April 03, 2008

Are You Ready for the Spring Monarchs?
By Ro Wauer

Already many of the monarch butterflies that have spent their winter in Mexico are passing through Texas in their spring migration. Texans should be seeing these marvelous creatures during all of April and May. Their second or third generation will continue their northward movement until they eventually reach the northern edge of their range, often as far north as southern Canada. Three or more generations will emerge each summer, each with a life span of four to five weeks. Those that emerge in late summer are not reproductively mature, so they represent the late season monarchs that migrate south through Texas to wintering sites in the mountains of Michoacan in central Mexico. There they gather in huge numbers to await springtime when they will begin their northward journey.

Monarchs are one of the “milkweed butterflies,” species that depend upon milkweeds for their larval foodplants. The similar but smaller queen butterfly is another of our milkweed butterflies, and one that we usually find throughout the summer and fall months. The milkweed butterfly name is derived from the fact that the females lay eggs only on milkweeds, although adults obtain food from a wide variety of flowers. Monarch eggs hatch in three to five days with warm temperatures, although eggs in cooler temperatures may not hatch for as many as 20 days. Upon hatching, the tiny caterpillars feed on the milkweed leaves, and as they grow from tiny caterpillars only few millimeters in length to about two inches they shed their skins five times, each known as an instar. The last instar fastens onto a safe place and pupates into a shiny green chrysalis, and in about ten days an adult monarch emerges.

One cannot help but marvel at monarchs, a seemingly fragile creature that can make a 3,000-mile fall journey from southern Canada to Central Mexico. The fall migrants generally follow one of two routes, either along the Gulf Coast or through central Texas. The largest numbers occur in wide belt from San Angelo to Bracketville to Eagle Pass during the second and third weeks of October. Those that pass through coastal Texas never reach the same high numbers, but some years are much better than others. But springtime monarchs are far more numerous along the Gulf Coast, passing through the Golden Crescent. They may fly at various elevations, usually in a gliding flight pattern. They often stop at flowering patches to feed, or when females discover milkweed plants they may take the opportunity to lay a single egg or a few eggs on the milkweed leaves. Once that has been accomplished, they continue northward, although they rarely survive much longer. It is that next generation that will continue their northward movement.

Although more than 100 kinds of milkweeds occur in North America, only a few can be found in South Texas. All of the milkweeds, almost all of the genus Asclepias, possess white sap that contains a toxic alkaloid. It is this material that milkweed butterflies absorb when feeding, either as a caterpillar eating the leaves or as an adult sipping nectar, that gives them toxicity that predators shun. A predatory lizard or bird, upon catching a monarch, will spit it out as soon as possible. And a few other butterflies, such as the viceroy, mimic monarchs. Viceroys are very similar in appearance to monarchs, but are not toxic. Viceroy caterpillars feed on willows, not milkweeds.

For those of us with gardens, now is the time to plant some milkweeds. The two species most commonly planted in our area include the native butterfly weed (Asclepias tuberose) and the nonnative tropical milkweed (Asclepias curassavica). Like feeding birds, providing a few milkweed plants can provide true satisfaction, knowing that we have helped the monarchs along their journey. Besides, we can entice them to stay a bit longer so that we can enjoy their beauty and appreciate their unique odyssey.

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